Technical Field
The present invention relates to time resolved emission circuit analysis and, more particularly, to timing analysis of emission events that are close in time and space.
Description of the Related Art
Analytical tools are commonly used for characterizing, testing, and debugging VLSI circuits. Some tools and techniques, such as emission tools based on off-state leakage currents and laser based stimulation tools, focus mostly on improving manufacturing process steps such as reducing leakage and variability, or improving performance and yield. Other tools and techniques, such as Time-Resolved Emission (TRE), focus mostly on probing time dependent signals from specific nodes and transistors of a VLSI circuits in order to understand its behavior and performances. Some faulty behavior of the chip may be investigated to understand the cause of faults and possibly guide process engineers or circuit designers to fix problems in new releases of the hardware.
Tester-based approaches for identifying emission sites significantly enhance device localization resolution. One tester-based approach is based on combining electrical stimuli tuning provided by automatic test equipment with optical characterization performed by emission tools. With image post-processing techniques, one can simplify localization and identification of devices that can be affected by electrical stimuli, such as clock frequency changes; logic state changes; switching activity (using time resolved emission measurements), etc. This whole process can be made in an interactive fashion. For the device that is interested, a test pattern can be generated to separate it from its neighbor devices using light emission.
However, devices that are close to one another in space and time can be difficult to resolve. Existing techniques for resolving such devices all have drawbacks. For example, one approach is to turn off one of the devices. However, in a complex circuit this may not be possible. Furthermore, this does not take into account the possibility that the absence of one of the signals (including all the circuitry before and after the switching gate of the interest) may significantly change the switching conditions of the remaining gate, for example by changing the power noise environment.